Polyomavirus BK-associated nephropathy after kidney transplantation: a single-center retrospective analysis

Polyomavirus BK-associated nephropathy is a challenging and increasingly recognized cause of kidney transplant morbidity and graft failure. Reported prevalence can vary significantly between centers, averaging 5%.

The paper reports the clinical and pathologic findings in five patients with BK virus-induced nephropathy. We performed a retrospective study including adult patients with graft dysfunction admitted to our department between 2010-2013. Clinical and biological data were obtained every month during the follow-up period. The biopsies were performed in case of graft dysfunction. All biopsy specimens were examined in light microscopy, immunofluorescence and electronic microscopy.

We studied 44 graft biopsies, and we found typical histological findings of polyoma BK nephropathy in five (11.4%) cases. All patients received immunosuppressive regimen based on calcineurin inhibitors, Mycophenolate Mofetil and Prednisone. Four of them were on Tacrolimus-based protocol and one patient was on Cyclosporine regimen. Age of transplant at diagnosis varied between 2 and 113 months (patient on Cyclosporine). In all cases, the BK virus nephropathy diagnostic was established taking into account histological findings, all patients presenting intranuclear viral inclusions seen on light microscopy and electronic microscopy. During the follow-up period, the renal dysfunction worsened in two of the five patients, one of them evolving towards ESRD, even though we minimized the immunosuppressive treatment and administered intravenous immunoglobulin.

The prognostic for BK virus nephropathy patients is reserved. Histological picture of BK virus nephropathy is similar to the one of graft rejection, differential diagnosis being difficult in the absence of viral inclusions evidence.